Hearing instruments or aids typically comprise a microphone arrangement which includes one or more microphones for receipt of incoming sound such as speech and music signals. The incoming sound is converted to an electric microphone signal or signals that are amplified and processed in a control and processing circuit of the hearing instrument in accordance with parameter settings of one or more preset listening program(s). The parameter settings for each listening program have typically been computed from the hearing impaired individual's specific hearing deficit or loss for example expressed in an audiogram. An output amplifier of the hearing instrument delivers the processed, i.e. hearing loss compensated, microphone signal to the user's ear canal via an output transducer such as a miniature speaker, receiver or possibly electrode array. The miniature speaker or receiver may be arranged inside housing or shell of the hearing instrument together with the microphone arrangement or arranged separately in an ear plug or earpiece of the hearing instrument.
A hearing impaired person typically suffers from a loss of hearing sensitivity which loss is dependent upon both frequency and the level of the sound in question. Thus a hearing impaired person may be able to hear certain frequencies (e.g., low frequencies) as well as a normal hearing person, but unable to hear sounds with the same sensitivity as a normal hearing individual at other frequencies (e.g., high frequencies). Similarly, the hearing impaired person may perceive loud sounds, e.g. above 90 dB SPL, with the same intensity as the normal hearing person, but still unable to hear soft sounds with the same sensitivity as the normal hearing person. Thus, in the latter situation, the hearing impaired person suffers from a loss of dynamic range at certain frequencies or frequency bands.
In addition to the above-mentioned frequency and level dependent hearing loss of the hearing impaired person loss often leads to a reduced ability to discriminate between competing or interfering sound sources for example in a noisy sound environment with multiple active speakers and/or noise sound sources. The healthy hearing system relies on the well-known cocktail party effect to discriminate between the competing or interfering sound sources under such adverse listening conditions. The signal-to-noise ratio (SNR) of sound at the listener's ears may be very low for example around 0 dB. The cocktail party effect relies inter alia on spatial auditory cues in the competing or interfering sound sources to perform the discrimination based on spatial localization of the competing sound sources. Under such adverse listening conditions, the SNR of sound received at the hearing impaired individual's ears may be so low that the hearing impaired individual is unable to detect and use the spatial auditory cues to discriminate between different sound streams from the competing sound sources. This leads to a severe worsened ability to hearing and understanding speech in noisy sound environments for many hearing impaired persons compared to normal hearing subjects.
Numerous prior art analog and digital hearing aids have been designed to mitigate the above-identified hearing deficiency in noisy sound environments. A common way of addressing the problem has been to apply SNR enhancing techniques to the hearing aid microphone signal(s) such as various types of fixed or adaptive beamforming to provide enhanced directionality. These techniques, whether based on wireless technology or not, have only been shown to have limited effect. With the introduction of wireless hearing aid technology and accessories, it has become possible to place an external microphone arrangement close to or on, i.e. via a belt or shirt clip, the target sound source in certain listening situations. The external microphone arrangement may for example be housed in portable unit which is arranged in the proximity of a speaker such as a teacher in a classroom environment. Due to the proximity of the microphone arrangement to the target sound source it is able to generate the external microphone signal with a target sound signal with significantly higher SNR than the SNR of the same target sound signal recorded/received at the hearing instrument microphone(s). The external microphone signal is transmitted to a wireless receiver of the left ear and/or right hearing instrument(s) via a suitable wireless communication link or links. The wireless communication link or links may be based proprietary or industry standard wireless technologies such as Bluetooth. The hearing instrument or instruments thereafter reproduces the external microphone signal with the SNR improved target sound signal to the hearing aid user's ear or ears via a suitable processor and output transducer.
However, the external microphone signal generated by such prior art external microphone arrangements lacks spatial auditory cues because of its distant or remote position in the sound field. This distant or remote position typically lies far away from the hearing aid user's head and ears for example more than 5 meters or 10 meters away. The lack of these spatial auditory cues during reproduction of the external microphone signal in the hearing instrument or instruments leads to an artificial and unpleasant internalized perception of the target sound source. The sound source appears to be placed inside the hearing aid user's head. Hence, it is advantageous to provide signal processing methodologies, hearing instruments and hearing aid systems capable of reproducing externally recorded or picked-up sound signals with appropriate spatial cues providing the hearing aid user or patient with a more natural sound perception. This problem has been addressed and solved by one or more embodiments described herein by generating and superimposing appropriate spatial auditory cues on a remotely recorded or picked-up microphone signal in connection with reproduction of the remotely picked-up microphone signal in the hearing instrument.